The application concerns granulated, alkaline dishwashing agent compositions that contain active chlorine and can be used in a mechanical dishwasher.
Alkaline cleaning agent compositions consisting mainly of builders, alkali metal silicates, alkali metal carbonates and/or alkali metal hydroxides, compounds containing active chlorine and, if desired, nonionic tensides usually are used for the washing of very soiled dishes by machine, especially in the commercial sector. The greater the content of active chlorine compounds in the cleaning agent compositions, the better the cleaning power for tea stains, for example, and the greater the content of alkali metal hydroxide, the better the cleaning effect, particularly for dishes with scorched food residues.
The cleaning agent compositions generally are prepared by the dry mixing of the individual powdered or granular constituents, for example, in rotating drums with the formation of the desired mixed product, where possible liquid components such as nonionic tensides and/or water glass are added as such, or as a mixture or in an aqueous solution, by spraying on the agitated powdered or granular constituents or groups of constituents, causing granulation. The compounds containing active chlorine generally are added at the end. A final product of a free-flowing, powdered or granular consistency that does not lump together during storage and is stable during storage with respect to its constituents is desired in any case. This applies especially to the compound containing active chlorine.
Polychlorinated cyanuric acids and their salts were found especially suitable as compounds containing active chlorine for powdered or granulated dishwashing agent compositions. Trichloroisocyanuric acid always is of great interest because of its highest content of active chlorine. However, its low solubility in water as well as its poor storage qualities are a disadvantage.
It is also known that powder and granulate mixtures become increasingly labile in storage, especially with a rising content of compounds containing active chlorine and alkali metal hydroxides. Under unfavorable storage conditions, for example, at elevated temperature and/or exposure of the packages to moisture, an exothermic spontaneous decomposition of the chlorine vehicle as well as reactions with other components of the cleaning agent composition take place. The cleaning agent composition remaining after the spontaneous decomposition is largely worthless since it sticks together and contains hardly any active chlorine. In addition, this possible spontaneous decomposition naturally represents an undesirable safety risk during storing and handling.
The recommendation was made in U.S. Pat. No. 3,166,513 to use potassium dichloroisocyanurate in granulated form with a critical particle size, as active chlorine component for the stabilization of dishwashing agent compositions with a content of compounds containing active chlorine. Potassium dichloroisocyanurate is considered more stable than the sodium dichloroisocyanurate, and the granulated form is said to provide additional stabilization. The amount of potassium dichloroisocyanurate does not exceed 5% by weight, in these products with a content of up to 30% by weight alkali metal hydroxides.
Potassium dichloroisocyanurate is considerably more expensive than the corresponding sodium compound, however. Thus the information of this patent specification is of theoretical interest only. Furthermore, the comment is made with respect to this patent in U.S. Pat. No. 3,352,785 that unjustifiable losses of available chlorine still occur despite a certain improvement with respect to the storing stability of these products, and formulations are mentioned therebefore that contain sodium dichloroisocyanurate of any desired granulation in the presence of nonionic surfactants and caustic alkalis, which are said to be more stable than cleaning agent compositions with content of granulated potassium dichloroisocyanurates, but the content of sodium dichloroisocyanurate is preferably 5% by weight maximum, even in this case.
A further increase in stability is said to be achieved according to U.S. Pat. No. 3,816,320 when the anhydrous sodium dichloroisocyanurate is replaced with its dihydrate. Its content can then be increased to 10% by weight. However, the dishwashing agent compositions prepared with it no longer contain free alkali metal hydroxide and, therefore, cannot be used for a technical comparison.
The preparation of cleaning agent compositions with a content of trichloroisocyanuric acid, which also are said to be stable in storage, also is known already from the U.S. Pat. No. 2,607,738, but again, these products do not contain any alkali metal hydroxide. This is understandable since it is known from "Soap, Cosmetics, Chemical Specialties," August 1974, pp. 46 to 55, particularly page 48, Table 3, for example, that trichloroisocyanuric acid is decomposed most strongly in the presence of sodium hydroxide flakes as an alkaline compound, as also is potassium and sodium dichloroisocyanurate.
There has been no shortage of experiments to make the use of trichloroisocyanuric acid possible by the concurrent use of stabilizing agents, such as
(a) dry trialkali salts of cyanuric acid or a mixture of equivalent amounts of cyanuric acid and alkali hydroxide (U.S. Pat. No. 3,178,372), or
(b) sodium acetate (U.S. Pat. No. 3,829,385).
However, these products contain undesirable ballast, such as cyanuric acid and sodium acetate in each case. The practical use of trichloroisocyanuric acid in dishwashing agent compositions with a high content of alkali metal hydroxides thus did not become acceptable although this substance has the highest content of active chlorine and, therefore, its application has always been tempting time and again.